U.S. patent number 4,242,498 [Application Number 06/028,300] was granted by the patent office on 1980-12-30 for process for the preparation of fluorine containing crosslinked elastomeric polytriazine and product so produced.
Invention is credited to Robert A. Administrator of the National Aeronautics and Space Frosch, Roger A. Korus, N/A, Robert W. Rosser.
United States Patent |
4,242,498 |
Frosch , et al. |
December 30, 1980 |
Process for the preparation of fluorine containing crosslinked
elastomeric polytriazine and product so produced
Abstract
New crosslinked elastomeric polytriazines have been prepared by
a 4-step procedure which consists of: (1) forming a
poly(imidoylamidine) by the reaction under reflux conditions of
anhydrous ammonia with certain perfluorinated alkyl or alkylether
dinitriles; (2) forming a linear polytriazine by cyclizing the
imidoylamidine linkages by reaction with certain perfluorinated
alkyl or alkylether acid anhydrides or halides; (3) extending the
linear polytriazine chain by further refluxing in anhydrous
ammonia; and (4) heating to cyclize the new imidoylamidine linkages
and thereby crosslink the polymer.
Inventors: |
Frosch; Robert A. Administrator of
the National Aeronautics and Space (N/A), N/A (San Jose,
CA), Rosser; Robert W. (San Jose, CA), Korus; Roger
A. |
Family
ID: |
21842673 |
Appl.
No.: |
06/028,300 |
Filed: |
April 9, 1979 |
Current U.S.
Class: |
528/362; 528/401;
528/422; 528/423 |
Current CPC
Class: |
C08G
73/0644 (20130101) |
Current International
Class: |
C08G
73/00 (20060101); C08G 73/06 (20060101); C08G
063/44 () |
Field of
Search: |
;528/362 |
Other References
Fluoropolymers, High Polymers, vol. XXV, 1972, Wall, pp. 267-289,
307-315..
|
Primary Examiner: Anderson; Harold D.
Attorney, Agent or Firm: McMillan; Armand Manning; John R.
Brekke; Darrell G.
Government Interests
ORIGIN OF THE INVENTION
The invention described herein was made in the performance of work
under a NASA contract and is subject to the provisions of Section
305 of the National Aeronautics and Space Act of 1958, Public Law
85-568 (72 Stat. 435; 42 U.S.C. 2457).
Claims
What is claimed is:
1. A process for preparing a crosslinked elastomeric polytriazine,
which comprises:
(a) forming a polyimidoylamidine by the reaction of anhydrous
ammonia under reflux conditions with a dinitrile compound selected
from the group consisting of perfluoroalkyl dinitriles having the
formula NC--(CF.sub.2).sub.p --CN, wherein p ranges from 2 to 18,
and the dinitriles of oligomeric and polymeric compounds having the
formula
wherein Y is fluorine or trifluoromethyl, p ranges from 1 to 18 and
m+n ranges from 2 to 7;
(b) forming a linear polytriazine by treating the
polyimidoylamidine with a ring-closing reagent selected from the
group consisting of the acyl halides and anhydrides of the
perfluorinated lower aliphatic acids containing up to about 12
carbons, and of the oligomeric and polymeric acids having the
formula
wherein R.sub.f is a perfluorinated lower alkyl group containing up
to about 3 carbons, Y is fluorine or a trifluoromethyl group, and y
is an integer within the range of 0 to about 50;
(c) extending the linear polytriazine chain by treatment with
anhydrous ammonia under reflux conditions to form additional
imidoylamidine linkages; and
(d) heating the extended polymer at a temperature within the range
of about 100.degree. to 200.degree. C. for a period of up to 4 days
to cyclize the imidoylamidine linkage and crosslink the polymeric
chain.
2. The process of claim 1, wherein the dinitrile used has an m+n
value within the range of 3 to 7.
3. The process of claim 1, wherein the reaction between the
dinitrile and the anhydrous ammonia is allowed to proceed for a
period within the range of about 4 hours to 4 days.
4. The process of claim 1, wherein the ring closing agent is
trifluoroacetic acid anhydride.
5. The process of claim 1, wherein the ring closing agent is
C.sub.3 F.sub.7 (CFCF.sub.3 CF.sub.2 O).sub.2 CFCF.sub.3 COF.
6. A crosslinked elastomeric polytriazine having the formula
##STR3## wherein (1) R.sub.f is a bivalent radical selected from
the group consisting of (a)-(CF.sub.2).sub.p -wherein p ranges from
2 to 18, and (b) oligomeric or polymeric radicals having the
formula
wherein Y is fluorine or a trifluoromethyl group, p ranges from 1
to 18 and m+n ranges from 2 to 7; and (2) R.sub.f.sup.1 is a
monovalent perfluorinated alkyl radical containing up to 11
carbons; x being an integer such that said polytriazine has an
average molecular weight M between crosslinks within the range of
10,000 to about 30,000, as measured by gel permeation
chromatography.
7. A polytriazine of claim 6, wherein R.sub.f.sup.1 is a monovalent
perfluorinated alkylether radical having the formula
wherein R.sub.f.sup.2 is a perfluorinated alkylgroup containing up
to 3 carbons, Y is fluorine or a trifluoromethyl group, and y is an
integer ranging from 0 to about 50.
8. The polytriazine of claim 6 or 7 wherein M is within the range
of 15,000 to 30,000, as measured by gel permeation chromatography.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to perfluoroalkylenetriazine polymers
and more particularly to a new method for preparing them.
2. Description of the Prior Art
Perfluoroalkylenetriazine polymers have been prepared heretofore by
two different methods, namely the acylationcyclodehydration of
imidoylamidines and the free radical coupling of preformed triazine
derivatives. However, these polymerization methods have so far
yielded polymer specimens that show disappointing material
properties [Fluoropolymers, High Polymers Volume XXV, edited by Leo
A. Wall, Wiley-Interscience (1972), pages 267 to 289 and 307 to
315; hereafter cited as Fluoropolymers]. In the case of the first
and most intensively investigated method, the imidoylamidine
approach, it has generally been found to be "very sensitive to
reaction conditions, afford poor reproducibility, and yield
polymers of molecular weights only marginally high enough for good
physical properties." (Fluoropolymers, page 288). In fact, this
approach is said to fail "because the ammonia liberated during
cyclization causes reorganization reactions, randomizing the
assimilation of mono- and difunctional compounds into triazine
rings, altering the functionality of the reaction system, and
leading to undesired cross-linking and shortened chains."
(Fluoropolymers, page 276). As to the second method, coupling of
preformed triazine rings, synthetic difficulties and poor
reactivity have led to polymers that are not elastomeric at room
temperature, due to the shortness of the chains between the
triazine rings (Fluoropolymers, page 280). In the circumstances,
the principal object of the present invention is to provide an
improved process which can yield the quality of polymer envisaged
by the pioneers in this art.
SUMMARY OF THE INVENTION
It has now been found that new polyperfluoroalkyltriazines that are
elastic at room temperature can be made by a new four-step process
which affords control of molecular weight and extent of
crosslinking in a reproducible manner. As compared to the materials
of the art, the new polymers have high molecular weights and
benefit from superior physical properties for elastomeric
applications, lower glass transition temperature, superior
hydrolytic stability, and broader use temperature range. The new
process disclosed herein is actually an improvement of the
imidoylamidine approach which involves (1) the reaction of ammonia
with a perfluorodinitrile, (2) the cyclization of the
poly(imidoylamidine) with an acyl anhydride or an acyl halide, (3)
a further chain lengthening reaction between ammonia and the
nitrile group terminated polytriazine molecules, and finally (4)
heat treating the latter product to cyclize the newly formed
imidoylamidine linkages and crosslink the polymer.
DETAILED DESCRIPTION OF THE INVENTION
The four reactions that constitute the process of the present
invention can be illustrated by the following formulas and
equations: ##STR1##
In the above formulas, R.sub.f represents identical bivalent
perfluorinated organic radicals or any combination of bivalent
perfluorinated organic radicals, said radicals being selected from
the group consisting of: --(CF.sub.2).sub.P -- wherein p ranges
from 2 to 18; and oligomeric or polymeric radicals prepared by the
reaction of a perfluorinated dicarboxylic acid halide with a
perfluoroepoxide and having the formula:
wherein Y is a fluorine atom or a trifluoromethyl group, p ranges
from 1 to 18, and m+n ranges from 2 to 7.
Instead of the trifluoroacetic acid anhydride shown in reaction II
above, other cyclizing agents may be employed including the
anhydrides, the acyl fluorides, and the acyl chlorides of the
perfluorinated lower aliphatic acids containing up to about 12
carbons, and of the oligomeric and polymeric acids having the
formula
wherein R.sub.f is a perfluorinated lower alkyl group containing up
to 3 carbons, Y is fluorine or a trifluoromethyl group, y is any
integer up to about 50. The proportions of cyclizing agent to
poly(imidoylamidine) are essential stoichiometric, although an
excess of the cyclizing agent may be employed if desired.
The molecular weight of the linear poly(imidoylamidine) formed by
reaction I is controlled to some extent by the reaction time which
can vary between about 4 hours and 4 days, depending on the
materials used and the conditions employed. The shorter reaction
times within these limits are preferred. The linear polytriazines
obtained from reaction II should typically have a molecular weight
of about 15,000 to 30,000 when the ring closing agent used is a
derivative of trifluoroacetic acid, said molecular weight
increasing so as to form an elastomeric network upon crosslinking
according to reaction IV.
In any event, the modulus of the final elastomer, i.e. the
crosslinked polytriazine, is dependent upon the average molecular
weight between crosslinks, M. The optimum value for M is one within
the range of 15,000 to 30,000. When M.ltoreq.10,000, the product is
cheesy and unacceptable, having a modulus greater than 10.sup.8
dynes/cm.sup.2. When M is .gtoreq.30,000, on the other hand, the
product is viscoelastic.
The reactions which constitute the process of the invention will
now be described in greater operational detail by means of the
following examples which illustrate, inter alia, the best mode of
practicing the invention and yet are not intended as limits to said
process. In these examples, all proportions and percentages are on
a weight basis unless otherwise indicated.
EXAMPLE 1
A triazine elastomer was prepared using the
.alpha.,.omega.-dinitrile of a perfluoroalkylene oxide as a
starting material. The dinitrile had the following formula:
##STR2## wherein m+n=6.
Reaction I.
The dinitrile, 33.84 g, was placed into a three-neck flask
connected to a Dewar condenser and to sources of nitrogen and
ammonia gas. The system was purged with nitrogen for ten minutes.
Ammonia gas was introduced under reflux conditions for 3 hours and
35 minutes. The ammonia was then vented and the flask sealed for 3
days with some ammonia remaining in it. A viscous polymer was
obtained having an intrinsic viscosity of 8.25 ml/g and a ratio of
IR absorbancies at 1600 cm.sup.-1 /2260 cm.sup.-1 of 41.
Reaction II.
The viscous polymer was dissolved in Freon 113,
1,1,2-trichlorotrifluoroethane. This solution was added slowly,
over a period of 15 to 20 minutes to an amber bottle containing
11.4 g trifluoroacetic anhydride. More anhydride, 2.0 g, was placed
in the flask to complete ring closure, and this was left standing
overnight. The Freon 113 was then removed by distillation, leaving
a residue which separated into layers. The upper layer, mainly
composed of trifluoroacetic acid, was removed with a Pasteur
pipette and the remaining material was placed in a vacuum oven at
90.degree. C. for 2 hours. The linear polytriazine thus obtained
weighed 35.92 g and had a weight average molecular weight of 23,000
as determined by high pressure liquid chromatography (HPLC).
Reaction III.
The linear triazine polymer was placed in a three-neck flask and
exposed to ammonia gas for 4 hours essentially in the manner of
reaction I. The flask was sealed and left overnight.
Reaction IV.
The viscous content of the flask was then heated from 130.degree.
to 200.degree. C. over a 4 day period to yield an elastomeric
product with a modulus of 10.sup.5 Nm.sup.-2 (as measured on a du
Pont thermomechanical analyzer, Model 943). The material had a
light amber color, was tacky, and had a high extensibility. On
heating at 300.degree. C. for 20 hours in air or nitrogen, a weight
loss of only 2% took place, as measured by thermogravimetric
analysis.
EXAMPLE 2
The method of Example 1 was repeated using the same reactants and
equipment, except for the following changes. In the preparation of
the imidoylamidine polymer (Reaction I), 2.6 g of the dinitrile was
reacted with ammonia gas under reflux conditions for 3 hours. After
this, the remaining ammonia was vented, the flask purged with
nitrogen, dry ice added to the condenser, and ammonia introduced
into the flask again. The flask was kept in a waterbath at
8.degree. C. for 3 hours and 15 minutes, i.e. until the dry ice was
exhausted. The ammonia was vented, leaving a viscous residue with
an intrinsic viscosity of 9.5 ml/g. IR analysis showed a very weak
nitrile peak at 2260 cm.sup.-1 and strong imidoylamidine peaks at
1520, 1600, and 1650 cm.sup.-1. The ratio of absorbancies at 1600
cm.sup.-1 /2260 cm.sup.-1 equalled 60.
Reaction II.
The linear polymer, 0.49 g, was placed in a flask with 0.15 g
trifluoroacetic anhydride and the mixture dissolved in 3 ml Freon
113. The solution was stirred overnight. More anhydride was then
added, 0.1 g, and the solution left open at room temperature for 24
hours to allow escape of the Freon 113. The flask was heated at
60.degree. C. under vacuum for 2 hours to remove volatile reaction
products. According to HPL chromatography, the linear polytriazine
had a weight average molecular weight of 28,000. The IR spectrum
showed no imidoylamidine peaks and a strong triazine peak at 1550
cm.sup.-1.
Reaction III.
The very viscous linear polytriazine was exposed to ammonia for 3
hours, as before. The flask was then closed with ground glass
stoppers and left overnight.
Reaction IV.
The very viscous gum-like material was heated under partial vacuum
(ca 0.5 atmosphere) from 110.degree. to 200.degree. C. over 5 days.
The resulting light amber gum had a modulus of 10.sup.4 Nm.sup.-2
and a sol fraction of 1.0. It was extremely tacky.
EXAMPLE 3
Again, the dinitrile was converted to poly(imidoylamidine) in an
excess of refluxing ammonia. When the average degree of
polymerization x, reached the range of 5 to 25, the material
dissolved in Freon 113 was converted to the polytriazine in an
amber bottle, using trifluoroacetic anhydride at a level >0.3
times the weight of poly(imidoylamidine). The solvent was distilled
off at 47.degree.-48.degree. C., the trifluoroacetic acid removed,
and the polymer heated to 90.degree. C. at 30 inch Hg with
continuous pumping for 3 hours. The linear polytriazine was treated
again with excess ammonia (reaction III) to yield an elastic
material which flowed at 110.degree. to 120.degree. C. This was
heated from 110.degree. to 140.degree. C. for 3 to 4 days to
crosslink and to 150.degree. C. to complete the process (reaction
IV). All procedural steps employed in this example, except those
just described, were identical to those of Example 1.
The molecular weight of the linear polytriazine obtained by
reaction II was 22,000, as measured by gel permeation
chromatography and viscometry. There is no change in molecular
weight with ring closure. The crosslinked material obtained had a
glass transition temperature of -45.degree. C., by differential
scanning calorimetry. Extraction in refluxing JP-4 fuel for 24
hours resulted in a 1% weight loss. The material exhibited thermal
stability in nitrogen and in air at 300.degree. to 350.degree. C.
with little or no change in elastomeric properties.
Thermogravimetric analysis in nitrogen showed a breakpoint about
330.degree. C.
EXAMPLE 4
Another preparation using the same materials employed in the
previous examples but limiting reaction I time to 38 minutes,
yielded a poly(imidoylamidine) with an IR spectrum ratio of
absorbancies at 1600 cm.sup.-1 /2260 cm.sup.-1 equal to 2 and an
intrinsic viscosity of 5.0 ml/g. Cyclization with trifluoroacetic
anhydride produced a linear polytriazine with a weight average
molecular weight of 8600. Chain extension and crosslinking at
100.degree. to 200.degree. C. over a 7 day period yielded a cheesy
material with a very low tear strength, low extensibility, and a
modulus of 10.sup.8 Nm.sup.-2.
EXAMPLE 5
The dinitrile used in Example 1, 53.8 g, was sealed in a glass
ampoule with a trace of anhydrous ammonia (.about.0.0006 mole).
After 7 days in a 225.degree. C. oil bath, a quantitative
conversion to a clear, cheese-like polymer was obtained.
EXAMPLE 6
The dinitrile of Example 1, 12.5 g (8.17 mmoles) was placed in an
addition funnel and added dropwise to flask containing 100 ml
anhydrous ammonia at reflux temperature. At the completion of the
addition, the excess ammonia was vented leaving an extremely
viscous liquid shown by infrared to be the diamidine. Freon 113, 50
ml, was added to the flask. Then more of the dinitrile, 12.5 g
(8.17 mmoles), was added dropwise to the stirred diamidine
solution. The solution was stirred for two more hours after
completion of the addition. At this time, infrared showed the
appearance of imidoylamidine bands and the disappearance of amidine
bands. A small portion, 5 ml, of this solution was treated with
excess trifluoroacetic acid anhydride, 5 ml, at 25.degree. C. After
the reaction mixture had been stirred overnight, the solvent was
removed in vacuo, leaving 2.0 g of thick syrup which showed only
triazine bands in the infrared spectrum.
EXAMPLE 7
The four-reaction procedure of Example 1 was followed again with
the principal change that an acyl fluoride was employed in reaction
II instead of trifluoroacetic acid anhydride. Other less
significant changes were made in materials and quantities, although
proportions were substantially preserved.
The perfluoroalkelene oxide dinitrile used was similar to that of
Example 1, except that its m+n value was 7. The dinitrile, 3 g
(1.61 mmoles), was placed into a 3-neck flask. Anhydrous ammonia
was purged into the flask for two hours to yield a product that
showed infrared imidoylamidine peaks at 6.09, 6.28, and 6.12 .mu.m.
Nitrile groups were also present as shown at 4.43 .mu.m. The
material was dissolved in 1,1,2-trichlorotrifluoroethane (Freon
113), 30 ml, and an acyl fluoride-C.sub.3 F.sub.7 O[CFCF.sub.3
CF.sub.2 O].sub.2 CFCF.sub.3 COF, 2 g, was added slowly from a
dropping funnel. All glassware was wrapped with aluminum foil.
After completion of the addition, the mixture was stirred
overnight. The linear polytriazine thus obtained showed a strong
triazine peak at 6.45 .mu.m.
EXAMPLE 8
This preparation again was essentially that of Example 1, except
that a perfluoroalkyldinitrile, [NC--(CF.sub.2)3--CN], was used and
perfluorocaprylic acid anhydride was substituted for
trifluoroacetic acid anhydride. The quantities were 2.02 g (10
mmoles) for the perfluoroglutaryl nitrile and 2.02 g (25 mmoles)
for the anhydride. The reactions were carried out as in Example 1,
proportions respected, to yield an elastomeric substance showing a
triazine peak at 6.45 .mu.m in the IR spectrum.
The crosslinked polymers prepared by the method of this invention
are tough, elastic, heat and chemical resistant substances which
can be used in many demanding applications such as fuel tank
sealants, O-rings, wire enamels, pneumatic ducts and edge
close-outs in aircraft, and so on. Other uses for the products, as
well as variations in the materials and procedures disclosed, can
be devised by the man skilled in the art without departing from the
spirit of the invention as described by the following claims.
* * * * *